1. Field of the Invention
The present invention relates to a tool battery pack which includes a monitoring section for inputting current signals of discharge current or charge current and for inputting voltage signals of cell batteries, and also includes a control microcomputer for performing discharge control or charge control of the cell batteries based on signals from the monitoring section.
2. Description of the Related Art
An existing tool battery pack relating to the above invention is described in Japanese Laid-Open Patent Publication No. 2009-097954.
The battery pack described in Japanese Laid-Open Patent Publication No. 2009-097954 is constructed such that discharge current or charge current is converted to a voltage signal by a shunt resistance and then the signal is input to a monitoring section. Further, the monitoring section is constructed to input voltage signal of each cell battery. The monitoring section transmits data of the discharge current or the charge current and also data of the voltage of each cell battery to a control microcomputer. The control microcomputer is constructed to perform discharge control or charge control based on the data transmitted from the monitoring section.
In the battery pack described above, the signal of discharge current or charge current is input to the monitoring section, and then the signal is transmitted to the control microcomputer through the monitoring section. Consequently, in case a failure of the monitoring section occurs and abnormal current flows, the failure of the monitoring section may not be detected unless the current value exceeds a normal range to a great extent. Therefore, the control microcomputer may perform discharge control or charge control based on erroneous current data, which causes damages of the cell batteries etc.
Further, even if abnormality of current is detected, it may be difficult to judge whether a failure of the monitoring section or the shunt resistance causes an abnormal current flow.
Thus, there is a need in the art to correctly judge a failure of the current detection element and the monitoring section of the tool battery.